Temperature control of individual tools in a cluster tool system

ABSTRACT

A temperature control unit for independent control of a number of independent channels, as can exist with a cluster tool used for semiconductor fabrication, has high efficiency, long term life and reliability, and requires only a small floor area. To these ends, the unit employs a single high capacity refrigeration system and disposes a number of separate temperature control channels for the individual tools, with only some channels receiving refrigerant. Low temperature channels use high pressure, sub-cooled refrigerant for chilling the heat transfer fluid to selected levels controlled by proportional valves adjusting refrigerant flow through evaporator heat exchanger units which cool heat transfer fluid. Moderate temperature channels cool the heat transfer fluid for associated tools to an ambient temperature level. The tools may, as needed, be heated by elements in the separate control channels, the control levels for both cooling and heating being determined by servo circuits programmed to measure actual and establish desired temperature levels.

FIELD OF THE INVENTION

[0001] This invention relates to systems and methods for controlling thetemperature of individual units and subsystems in a system, and moreparticularly to a compact and versatile system and method forindividually controlling the temperature of different tools in asemiconductor processing system.

BACKGROUND OF THE INVENTION

[0002] Many production processes maintain control of the temperature ofindividual units or elements within an overall system by refrigeratingor heating the individual units during operation of the system. Aparticularly noteworthy and critical example of the type of demandingenvironment in which precise temperature control is needed is found insemiconductor fabricating processes. The manufacture of integratedcircuits by forming multiple replicated patterns on semiconductor wafersinvolves numerous successive steps. Following image replication, intenseenergy concentrations are used to etch, deposit and otherwise treatsuccessive layers on the wafer, but at the same time precise placement,alignment and dimensional stability of the wafer must be maintainedduring practically all such process steps. Furthermore the final productcannot accept even minuscule defects even though temperaturedifferentials can tend to distort wafers, affect alignments anddeteriorate pre-existing layers. Given these and other considerations,semiconductor fabrication facilities require vast capital expendituresto provide tools and support equipment meeting the conflicting demandsof quality control and high volume output at the levels of resolutionnow demanded by the state of the art.

[0003] An example of one type of semiconductor fabrication equipment nowin wide use is the cluster tool, in which different closely juxtaposedtools are used, singly or in combination, to transport, position, andcomplete different ones of a succession of processing steps quickly andefficiently. The tools within the cluster can vary widely in purpose andfunction. Some tools in the cluster may have to be refrigerated at timesto levels as low as −40° C., while at the same time others may have tobe heated to levels as high as 80° C. to 100° C. The levels will varyduring a process, but at any given time, the then chosen temperaturelevel must be maintained closely at each operative tool. In addition,abrupt temperature changes are sometimes needed. For instance, extremelyrapid cooldown of a tool at a transition point in a procedure may meanthat the overall process can be significantly shortened or substantiallymore efficient. If transition times can be markedly shortened for toolswhen they are within an evacuated process chamber, the same chamber canbe used again for a different step, without the need for returning thechamber to ambient pressure and reestablishing the vacuum, or utilizinga second chamber for the subsequent processing step.

[0004] The different tools in a cluster have heretofore largely beenrefrigerated or heated by individual units, each using a separate primerefrigeration source with a compressor/condenser system, or a separateheater. This not only affects reliability by increasing the number ofcritical and active operating units, but also requires that asubstantial amount of floor space be dedicated to the cluster tool.However, every square foot of area required in a semiconductorfabrication facility is extremely costly. A large “footprint” size thusimposes a substantial economic penalty. Modern temperature control unitsfor a cluster tool having, for example, six tools, require in the rangeof 18 square feet or more of floor area. Moreover, the service lifetimeof these systems is limited because of the need to use multiple smallrefrigeration units, since they have shorter lifetimes than larger unitsand offer more chances of failure.

[0005] On-line maintenance of cluster tools requires that they beflushed of heat transfer fluid and disconnected from the temperaturecontrol unit. Current approaches typically use quick disconnects, whichallow fluid to spill, and which tend to leak after a number ofoperations and impose a significant pressure drop in the system. Anefficient subsystem for flushing and filling fluid used in temperaturecontrol is therefore highly desirable.

[0006] Precise control of the temperature of refrigerant-cooled fluidover a long service life is a desirable goal seldom achieved inpractice. Solenoid valves, bimetallic proportional valves and othercontrols often used have inherent wear and hysteresis problems whichaffect both their accuracy and long-term life. Thermal expansion valvesare capable of better resolution and proportional control, but presentnew problems when used in a refrigeration system for cluster tools,since it is the tool temperature which must be regulated, not superheatas in prior systems. In addition, prior thermal expansion valve systemsare not usually able to effect extremely rapid cooldown because ofthermal inertia problems.

SUMMARY OF THE INVENTION

[0007] A system in accordance with the invention concurrently operates anumber of thermal control channels for thermal transfer fluid, eachchannel having both cooling and heating capability for adjusting thetemperature of an associated process device. This system advantageouslyserves as a compact multi-channel temperature control unit for thedifferent tools in a cluster tool.

[0008] In accordance with the invention, individual tools in a clustertool used in semiconductor wafer processing are differently temperaturecontrolled by control loops circulating selectively heated or cooledthermal transfer fluid. The control loops respond to sensors whichmeasure actual tool temperatures and include circuits for providing thesignals for regulating thermal transfer fluid temperature. Thosechannels requiring significant chilling receive a subcooled,high-pressure refrigerant from a single refrigerator unit having a totalrefrigeration capacity sufficient to meet the total demands of all thetools. A high pressure refrigerant, after compression, condensation andsubcooling, is fed out in separate lines to the different control loops,where pressurized heat transfer fluid is circulated through the tools.The control of refrigerant flow to each different evaporator in the loopdetermines the amount of refrigeration capacity used to cool the heattransfer fluid and hence the tool. Thereafter, the expanded refrigerantis returned to the single refrigeration unit.

[0009] Further, in accordance with the invention, all channels in amulti-channel system circulate thermal transfer fluid replenished from asingle pressurized tank in separate control loops including thepressurizing pumps, heat exchangers and heaters. The low temperaturechannels incorporate compact evaporator/heat exchange units controlledby thermal expansion valve units which are arranged to respond to tooltemperature and also to prevent astable operation. Where only moderatecooling need be supplied to a tool, the heat exchangers in therespective channels receive only utilities water or other cooling mediumat some ambient temperature. The heaters in the control loops areenergized to raise the temperature of the heat transfer fluid when thetools are to be operated at temperatures above ambient.

[0010] The channels are configured with flow control valves which allowdisconnection of the lines to any tool for service. The lines for heattransfer fluid that couple to and from the tool are disposed with atleast one low point below the tool level, and include purge valvescoupled to the low point and the vicinity of the tool. The temperaturecontrol unit includes separate lines coupled to the pressurized tankfrom each control channel. A pressurized source of purge gas is usuallyreadily available for use in flushing. The entire loop section thatincludes the lines to and from the tool and the tool itself iseffectively purged by using the purge gas to force heat transfer fluidthrough the tool from the low point and into the pressurized tank. Thereturn line can further be purged in an opposite direction back throughthe return coupling to the pressurized tank. The tool can then beserviced or replaced and reconnected. To refill the lines and the toolwith heat transfer fluid, the pressurized fluid source, which may beaugmented by purge gas pressure, is coupled into the lines and into thetool as the flow control valves are held open and a point is vented toatmosphere. This mode of operation and configuration greatly facilitatethe flush and fill functions, both in terms of reducing time andeliminating the often substantial leakage and dispersion of heattransfer fluid around the area.

[0011] A feature of this arrangement is that only a single largerefrigeration system in used to cool a fluid in the different number ofchannels. Such an approach greatly reduces the parts count, whileincreasing the reliability of the system because large refrigerationsystems are inherently more reliable than smaller units. In addition,the single refrigeration unit incorporates elements and subunits whichimprove its efficiency and reliability, such as a subcooler forinterchanging thermal energy with low pressure suction return gases, aninjection capillary system, a hot gas bypass and a superheater expansionvalve system, as well as gas filter and oil separator devices. There ismore efficient use of space because the total volume required is lessthan what individual units would require for the same capacity.

[0012] In addition, this system substantially reduces the critical floorspace area that is needed because all the subsystems may be compactlydisposed within an open sided frame having a small area base. An arrayof pumps and closely spaced in-line motors are mounted within the upperpart of the frame. The compressor for a high capacity, high efficiencyrefrigeration system is disposed within the frame alongside and lowerthan the pump/motor array. Other units in the refrigeration system aredisposed below and alongside the array. An accumulator vessel and apressurized tank for heat transfer fluid are placed at opposite sides ofthe frame. A row of heat exchangers and flow controls for the chilledloops are disposed side by side below the array. Inlet and outlet portsand conduits for interconnection to the lines running to the tools andutility water are all accessible at an open side of the frame. Thepump/motor combinations for the chilled channels can be disposed in theinterior of the frame, for better isolation from ambient temperatureeffects. With the inlets, outlets and valves all accessible from the oneside, manual connections, including manual connections of fluid and gaslines, and manual controls are all conveniently available. Manifolds areused to distribute cooling water, refrigerant, and heat exchange fluidfrom common sources to the different channels. For the unchilledchannels, small heat exchangers are disposed on the opposite side fromthe open frame, alongside the pump/motor array. The replenishment andpurge line are small and woven throughout the system. All chilled unitsand lines are covered with insulation extending out to the exteriortools. The footprint for a unit having three total channels, one or twoof which can be chilled to −40° C., is less than 0.6 ft.² per channel. Afootprint of 12″×34″ has also been realized for a system with greaterthan 4000 watts cooling capacity at −40° C., and which includes threemoderate temperature and three low temperature channels.

[0013] The proportional valve systems are of a long lifetime thermalexpansion valve type that has no wearing or frictional parts andprovides precise proportional control. However, the tool temperaturethat is sensed is not directly controlled, since in this system, controlis at the input to the evaporator/heat exchanger. If the sensed tooltemperature demands a response beyond the capacity of the evaporator,then the evaporator efficiency may enter an astable phase in whichevaporator output increases rather than declines, so that further valveopening decreases rather than increases chilling. The evaporator outputmay also contain liquid refrigerant, a condition to be avoided at thecompressor. The problem is obviated in one example by employing areference evaporator in parallel to the chilled channels, andcontrollably heating pressure bulbs thermally coupled to the referenceevaporator but communicating with flow control valves in the differentchannels. In addition, parallel flows from the evaporator outputs may becombined and the return flow temperature to the refrigeration unit usedto limit flow to assure that excessive refrigerant flow will not bedemanded. In a second version of an improved thermal expansion valvesystem for controlling multiple channels, superheat temperatures aremeasured at each evaporator, including the reference evaporator, and thecontroller is used to diminish heater temperatures in inverse relationto the difference between the individual evaporator output levels andthe reference evaporator output level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A better understanding of the invention may be had by referenceto the following description, taken in conjunction with the accompanyingdrawings, in which:

[0015]FIG. 1 is a block diagram representation of an exemplary systemfor multiple channel cooling in accordance with the invention;

[0016]FIG. 2 is a block diagram of a single, large capacity,refrigeration unit for feeding a subcooled, high-pressure stream to lowtemperature channels in the system of FIG. 1;

[0017]FIG. 3 is a block diagram representation of elements employed inchannels in which the tool is to be maintained in a low temperaturerange, showing further details thereof including an improved thermalexpansion valve system for the low temperature channels;

[0018]FIG. 4 is a perspective view, simplified as to some lesserdetails, of the physical layout of a practical multi-channel,temperature control unit in accordance with the invention, showing howthe desired compact, low footprint combination is achieved;

[0019]FIG. 5 is a block diagram of an alternate arrangement for stablyoperating multiple thermal expansion valves while also enabling rapidtool cooldown;

[0020]FIG. 6 is a fragmentary perspective view of the principal elementsof a flush and fill subsystem in accordance with the invention; and

[0021]FIG. 7 shows an alternative arrangement of the system inaccordance with the invention for providing different combinations ofchilled and unchilled channels while at the same time preserving thedesired low area footprint.

DETAILED DESCRIPTION OF THE INVENTION

[0022] A practical example of the system in accordance with theinvention is described as used in conjunction with a cluster tool forsemiconductor fabrication that requires six different control channels.Each channel typically is used to hold its associated tool atpredetermined temperature levels at different points in its operativecycle. In FIG. 1, to which reference is now made, a multi-channeltemperature control system 10 having six different channels employs asingle refrigeration system 12 including a compressor 14 and condenser16 receiving a conventional cooling medium (such as air or a liquidcoolant). The refrigeration system 12 includes a number of functionalsubsystems, described below in conjunction with FIG. 2, which improveefficiency and insure longer life. The compressor 14 is from 6 Hp to 10Hp capacity in this example, since it is desired to provide in the rangeof 4000 watts cooling at −40° C. An environmentally safe refrigerant,such as R22 or R507, is subcooled to approximately 10° C., providing ahigh pressure subcooled stream (approximately 200 psi) to a manifold 20for feeding the different channels of the unit. R507 is preferred, sinceit provides greater refrigeration capacity than R22.

[0023] A cluster tool 25, shown only diagramatically, incorporates anumber of individual tools 28 a, 28 b, . . . 28 f. For purposes of thisillustrative example, the tools 28 a to 28 f are alike with respect totemperature control, each having an inlet 30 and outlet 32 and internalpassageways (not shown) for circulating a thermal transfer fluid whichheats or cools as required at a particular time. The thermal transferfluid (such as a perfluorinated compound, a glycol or a glycol and watermixture commercially available under different trademarks) is returnedto the associated control system, described below, for the requiredtemperature adjustment. One or more sensors 34, each in thermalinterchange relation with a different individual tool 28 a, 28 b. . . 28f, generate separate signals indicating the temperature levels of theindividual tools 28 a. . . 28 f. A control system 40 providing closedloop servo control of the individual channels includes one (or more)central processor units (CPUs) 42 which use programmed reference signalsto establish target temperatures for the individual servo controls 44a-44 f. The servo controls 44 a-f are each associated with a differentcontrol channel (I through VI) and provide two available control signalsfor each different channel. One control signal (T_(h)) operates a heaterdevice and the other control signal(T_(v)) operates a refrigerationcontrol valve, these signals being differentiated by channel subscripts1, 2 . . . 6. Thus for channel I, the signals are T_(v1) and T_(h1). Thedifferent servo reference signals are established by tool temperatureprograms in the CPU 42. Servo error signals are generated within theservos 44 by comparison of the reference signals to the inputs T_(I). .. T_(VI) from the different temperature sensors 34. These servo loopscan be integrated into the CPU 42 but are shown as separate for clarity.

[0024] In the multi-channel temperature control system 10, theindividual control channels are divided into two sets, here each threein number. The members of a first set, called “low temperature channels”50, 51, 52, each receive not only the control signals (e.g., T_(v2) andT_(h2)) but also the subcooled, high-pressure stream of refrigerant fromthe supply manifold 20 and the heat transfer fluid in the flow loop tothe tool. A single pressurized fluid tank 60 provides the heat transferfluid to all the channels.

[0025] The low temperature channels not only provide substantialrefrigeration capacity, to lower the temperature to as low as −40° C.,but also may heat the tool to 80°-100° C. on demand. The “moderatetemperature” channels 55, 56, 57 in the second set receive the heattransfer fluid from the tank 60 and water from an ambient source,usually an available utility, but do not use refrigerant. The moderatetemperature channels thus provide cooling to the ambient temperaturelevel, or heating as high as 80°-10020 C.

[0026] All channels include valves 61, 62 at their output and returnconnections for control of heat transfer fluid flow to and from theassociated tool. In addition, the channels include gas purgeconnections, as described below in conjunction with FIG. 6, so that theheat transfer fluid can be flushed for disconnection and maintenance ofthe tool and then the system can be refilled. Once filled, the fluidloop is essentially closed, although leakage can be compensated byreplenishment of fluid from the pressurized tank 60 through a separateline to a T-connection 64 in the return valve 62.

[0027] Within a given low temperature channel, such as that numbered 50(channel I), as shown in FIG. 1 and the more detailed diagram of FIG. 3,the subcooled, high-pressure stream from the refrigeration unit 12 issupplied via a proportional control (thermal expansion or “TXV”) valve65 to the evaporator in an evaporator/heat exchanger combination 67. Theexpanded gas applied to the evaporator/heat exchanger 67 thus cools thethermal transfer fluid to that level established by the thermalexpansion valve 65. A pressurizing pump 69, driven by a closely spacedcollinear motor 72, and surrounded by insulation 74, receives returnfluid from the outlet 32 (FIG. 1 only) of the associated tool. The pump69, preferably of the regenerative turbine type, pressurizes the heattransfer fluid as it gives up heat to the evaporator/heat exchanger 67in the channel, if cooling is needed. An electrical resistance heater 76is also in the flow channel, and responsive to control signals (T_(h))to heat the fluid to a higher level tool temperature specified by thecontrol program.

[0028] The proportional flow control or thermal expansion valve 65 usedin the system is a stable, frictionless, highly reliable thermalexpansion unit that provides sensitive control of flow through a widedynamic range. In the body of a proportional flow control valve such asthe TXV 65, a flexible diaphragm forms one wall of a confined volumethat is filled with a pressurized gas. The interior of the confinedvolume in the valve 65 communicates with a separate closed bulb via asmall conduit. Flexure of the diaphragm in the valve 65 in response topressure changes within the bulb shifts the position of the diaphragmand a coupled movable valve element which receives refrigerant from aconduit, thus increasing or restricting flow as commanded. The commandpressure is determined by the setting of a heater coil about or adjacentthe bulb, which setting corresponds to the desired temperature for thetool. The thermal exchange between the bulb and an associated coldsource is attenuated by an interposed insulation. As described in apending application of Richard Petrulio et al. entitled “Expansion ValveUnit” , Ser. No. 08/555,001, filed Nov. 9, 1995, the heating of the bulbenables rapid adjustment of the target temperature and therefore theflow into the evaporator. The insulation effectively integratesmomentary variations in evaporator output temperature, which can beconsiderable, and which would otherwise introduce a short term variable.

[0029] Usually, the bulb coupled to a proportional flow control valve 65is in conductive contact with the element or conduit whose temperatureis to be directly regulated, such as the superheat temperature at anevaporator. Here, however, the sensed temperature is that at therelatively remote tool, not the evaporator output. One cannot assumethat the response characteristic is monotonic. Refrigeration cycles, infact, become astable and the compressor can be damaged if the evaporatorreceives so much refrigerant that it delivers a gas-liquid mix. Insteadof greater cooling with increased flow the refrigeration output thendecreases. A point is thus reached at which further opening of the valveno longer is wanted, since calling for more refrigeration for the toolis self-defeating. In accordance with the present invention, thesubcooled refrigerant from the refrigeration unit 12 is applied to theseparate lines to the different low temperature channels 50, 51 and 52.

[0030] The disposition of the elements in each of the channels beingessentially alike, only that in channel I (50) is shown in detail.Referring to FIG. 3, the refrigeration unit 12 is essentially that whichis shown in a different figure (FIG. 2) and the compressor 14 is shownin dotted line form because it is important to the functioning of theunit to avoid the return of liquid refrigerant to the compressor (the“flood condition”). Energy is conserved by using the subcooler 81 in aheat exchange function to interchange thermal energy between the colderreturned gases and the high pressure, but moderate temperaturerefrigerant exiting from the refrigeration unit 12, prior to expansion.

[0031] At the reference evaporator 82, the input refrigerant is providedvia a capillary 83 which, in known fashion, provides maximum expansion,lowering the output of the evaporator to a minimum, here about −50° C.The reference evaporator 82 is small and because it is not subjected toa thermal load of any significant amount, there is virtually nosuperheat or likelihood of a flood condition.

[0032] The output temperature is sensed by a reference thermocouple 84which feeds a signal to each settable “flood” comparator 85 in threeself-limiting load temperature controllers 86 a, 86 b, 86 c. This ismuch more than a comparator, because it can be set to give a signalwhich varies in accordance with the difference between two other signalsreceived as inputs (usually from thermocouples). This can be acommercially available “Watlow Series 965” controller from WatlowControls, Winona, Minn. that provides a pulse with modulated output thatrepresents the difference between the signal from the referencethermocouple 84 and a signal from a “flood thermocouple” 87, whichrepresents the output temperature in the return line to therefrigeration unit 12 from the main evaporator 67 (see also FIG. 1) inthe controller 86 a.

[0033] This output line is joined with the output from the referenceevaporator 82, but the conduit 88 is preferably made of a low heatconductive metal, such as stainless steel, so that the temperaturedifference does not cause significant heat transfer along that length ofconduit. Furthermore, the flood thermocouple 87 is positioned on theunderside of the output line 88 close to the evaporator 67, because ifliquid is present in the two-phase refrigerant, it will be on the bottomof the line and thus the sensed temperature will be more sensitive tothe presence of the liquid.

[0034] The specific value which the settable flood comparator 85 isattempting to respond to is the difference between the −50° C. typicallysensed by the reference thermocouple 84 and a lesser value sensed by theflood thermocouple 87. If the superheat of the evaporator 67, i.e., theincrease in temperature across the evaporator 67 as it interchangesthermal energy with the load (load I of FIG. 1) is high, there is nodanger of a flood condition. If the temperature difference between theevaporator 67 and the reference evaporator 82 outlets decreases down toabout 35° C., however, then the system starts restricting the thermalexpansion valve 65 that controls flow into the evaporator 67, if thetemperature command T_(v1) at the load calls for more refrigeration.When the temperature difference becomes only 10° C. (i.e., theevaporator refrigerant output is at −40° C.), then the invention shutsthe thermal expansion valve 65 completely. This is done by comparing theload temperature command to the signal from the settable floodcomparator 87, using the two inputs to a settable main comparator 89. Atthe limit conditions, the load temperature becomes immaterial and morerefrigeration is needed to avoid the flood condition. The settable maincomparator 89 controls the heater 82 a which adjust the temperature andtherefore the pressure at the sensing bulb 82 b which regulates thethermal expansion valve 65.

[0035] The input from the flood settable comparator 87 is a pulse widthmodulated signal, and to avoid erratic operation, this is signal timeaveraged by an integrator circuit 90 before application as an input tothe settable main comparator 89. Then, the settable main comparator 89provides a heating control signal to the resistance heater 82 a with theobjective of preventing the evaporator 67 outlet temperature fromdropping below −33° C.

[0036] Thus, in the thermal expansion valve 65, as long as no floodconditions exist at the evaporator 67 output, the settable maincomparator 89 controls the heater 82 a which changes the pressure in thethermal expansion valve 65, allowing the thermal expansion valve 65 toopen and close so as to supply refrigerant flow to the evaporator 67. Ifthe evaporator 67 does not superheat enough and its temperature drops towhere flooding might occur, then the restriction on the output of thethermal expansion valve 65, until it is finally shut down if the floodthermocouple 85 senses a temperature of −40° C.

[0037] A single reference thermocouple 84 is used with other bulbs andother heaters for the second and third self-limiting load temperaturecontrollers, even though such bulbs and heaters are not shownseparately. As in the pending application of Richard Petrulio et al.entitled “Expansion Valve Unit”, Ser. No. 08/555,001, filed Nov. 9,1995, insulation is disposed between the bulb and the adjacent source ofcold, so as to slow thermal energy transfer to eliminate suddentransitions in pressure and also to limit heating of the referenceevaporator 82.

[0038] The second and third controllers can, in this version,independently control the associated loads (II and III) withoutinteraction with the other controllers in the group.

[0039] In the moderate temperature channels, as in that numbered 55(channel IV) referring again to FIG. 1, the amount of refrigerationneeded is less, since the tool is usually operated hot, although it maysometimes have to be cooled quickly to ambient level for service orchanging fabrication modes. At the lower limit this temperature willtypically be the temperature of available water from local utilities.This ambient coolant is supplied to the heat exchanger 100 in thechannel from an external source (not shown). Under the statedconditions, a solenoid valve 102 in the coolant flow path providesacceptable control of tool temperature by on-off operation. However, aproportional control valve can be used if long life, high precisionoperation is desired.

[0040] The moderate temperature channels are each pressurized by theirindividual compact collinear motor 72 and pump 69 combination, butinsulation is typically not utilized. As in the low temperaturechannels, a resistance heater 76 is in the flow system to raise thetemperature of the fluid to as much as 80° C. to 100° C. An electricalresistance heater is not the only type of heater that might be employedbut satisfactorily meets the long lifetime, low cost and highperformance characteristics desired for the system.

[0041] A high efficiency but compact single refrigeration system isdepicted in general form in FIG. 2, which shows the compressor 14,condenser 16 and the path by which high pressure, subcooled refrigerantis supplied via the refrigeration supply manifold 20 to the associatedlow temperature channels. Starting at the compressor 14, outputrefrigerant after compression passes through the condenser 16, which iscooled by conventional means, here water from an available utility, andis directed through a subcooler 120, in counterflow relation to lowpressure suction return flow provided from a refrigerant receiver tank123. The outgoing refrigerant passes through an accumulator 122 to therefrigeration manifold 20. In the subcooler 120, the cooled low pressuresuction return is therefore used to subcool the refrigerant whileincreasing in pressure passing through a filter 124 and oil separator125 before reaching the compressor 14 input.

[0042] A number of other expedients are used for additional safety andefficiency. The cooled, high pressure output from the condenser 16 isfed back into an injection capillary tube (not shown) in the compressor14 for automatic cooling. The same output is also directed into theinput line to the compressor 14, through a desuperheater expansion valve128, thus drawing off a portion of the refrigerant flow when the maximumrefrigeration output is reached. A more direct loop between thecompressor 14 output and input is provided by a hot gas bypass valve 130and a serially connected solenoid valve 132. Thus, if the pressurizedoutput from the compressor 14 is at too high a temperature, a portion ofthis flow is routed back to the input via the solenoid valve 132. Thisbypass loop is selectively shut off by closing the solenoid valve 132.The individual units in this single refrigeration system actautomatically, apart from the solenoid valve 132, which has a low dutycycle in any event.

[0043] This example of a single high efficiency refrigeration unit isprovided along with a specific depiction of a practical system todemonstrate that severe operational requirements and volumetricconstraints can concurrently be satisfied.

[0044] Given the fact that three or more tools are to be chilled to lowtemperature by this single refrigeration system, the neededrefrigeration capacity can still be provided considerably moreefficiently than by separate small units. The refrigerant is conductedessentially through three independent control loops or branches beforereturning to the single system with its advantageous internal filtrationand oil separation, and other expedients such as bypasses, feedback andshutoffs for improving safety factors and increasing internalefficiency. Thus with a 10 horsepower compressor, the total coolingcapacity at −40° C. can exceed 4,100 watts, and substantially greaterlevels of cooling capacity can be reached if the lowest temperatures canbe raised.

[0045] This system has the versatility to be used with a variety ofcluster tools so as to provide the needed spectrum of temperaturecontrol conditions, even though in other instances the mix of moderateand low temperature channels might be somewhat different. If so, it isevident that the same principles can be utilized even though the numbersof individual channels in the mix will be altered.

[0046] In operation, as the refrigeration unit 12 is continuouslyoperating to provide subcooled refrigerant to the low temperaturechannels 50, 51, 52, pressurized heat transfer fluid is passing, atselected temperature levels dependent upon the processing cycle, throughthe corresponding first three tools 28 a, 28 b and 28 c. Concurrently,heat transfer fluid is passing through the remaining three tools 28 d,28 e and 28 f via the moderate temperature channels 55, 56, 57.Previously set temperatures are maintained by use of the proportionalcontrol valve 65 in the subcooled refrigerant line feeding theevaporator/heat exchanger 67 in the first low temperature channel 50,for example In the moderate temperature channels, such as the fourthchannel 55, while the heat transfer fluid flows through the heatexchanger 100, the utilities water flow is controlled in on-off fashionby the temperature control signal applied to the associated input valve102. Thus the temperature of the heat transfer fluid and the tool can belowered rapidly. In most instances, steady state operation of themoderate temperature channels will be at above ambient temperature andthen when there is a process transition, the tool will be cooled asquickly as allowable to ambient temperature.

[0047] Individual electrical resistance heaters 76 are incorporated inthe low temperature channels, and similar heaters 76 are separatelyincluded in the moderate temperature channels as well. These heaters 76enable the temperature levels to be brought to the desired maximumrange, up to no more than about 100° C. in this example.

[0048] Even though the temperature control unit is designed forlong-term continuous operation, the system incorporates means fordisconnecting the fluid lines in the control channel from the tool towhich it is coupled. Such disconnection is primarily for purposes oftool maintenance, reconditioning or replacement. Flushing the heattransfer fluid out of the system, and later refilling the system, isgenerally done only cumbersomely in the prior art. Quick disconnectcouplings that are employed tend to leak, particularly after a fewcycles of use. They also inevitably involve spillage and also introducea substantial pressure drop in the lines. The present system includes aflush and fill arrangement described below that performs these functionsin a rapid, controlled and simple manner.

[0049] In accordance with the invention, referring now to FIG. 4, theneeded refrigeration capacity, pumping, control and heat exchangefunctions for interaction with the individual tools have all beenaccommodated within a single open and compact mechanical frame 140. Theframe 140 is of simple rectangular form in this example although itcould be of other geometries and is mounted, as shown, on rollers formobility. The floor area commitment is substantially lower than priorsystems have heretofore required. In the practical example shown, thefloor area covered is only 12″×34″, while the height of the frame itselfis only 34″. The shallow depth and relatively short frontal lengthenable the assembly to fit into close quarters on the floor of afabrication facility. For purposes of description, the exposed broadside of the frame 140 in FIG. 4 will be referred to as the “front” .

[0050] The motor 72 and pump 69 combinations are disposed within theframe 140 along spaced apart but parallel horizontal axes in an arraythat principally occupies one upper corner of the frame 140. The motors72 are directly coupled to the collinear pumps 69, through a shortinsulating spacing, with the ends of the pumps 69 lying essentially inthe same plane, and in the front to back direction. The interior volumeoccupied by this array locates the pump 69 ends in an accessible frontplane along a broad vertical side of the frame 140. Thus, lineconnections can be made at this side, and servicing can be accomplishedreadily because of easy accessibility to virtually all interiorcomponents. In this example, the three low temperature channels 50, 51and 52 including the three evaporator/heat exchangers which areside-by-side, are within the interior of the frame 140, while thepump/motor combinations for the moderate temperature channels 55, 56, 57are directly above, immediately below the top of the frame 140. Thepumps 69 in the low temperature channels 50, 51, and 52 are thus lessexposed to the working environment, and insulation 141 about them isthereby more effective.

[0051] The input and output couplings for connection to the associatedtools (not shown) are disposed in a second distributed arrayhorizontally adjacent the pump/motor combinations, with the connectorends being closest to the plane of the access side. For example, for thelow temperature channels, the return couplings 142 are along ahorizontal axis in the mid-region of the frame 140. The outlet couplings144 are along a lower horizontal level somewhat above the base. Both arecovered by insulation 141. These couplings include manually operablevalves and T-connections for coupling to feeder lines, full details ofwhich are not shown in FIG. 4 in order to avoid overcomplicating thatFigure. Similarly, connections for the supply and return of utilitieswater, located at the right bottom portion of the access side, wiringand control circuits, and various other small and detailed features, areshown either diagrammatically or not included, to avoid excessivedetails and explanation of features that are self-evident once the basicgeometry is understood.

[0052] Primarily, it must be understood that FIG. 4 shows the principalelements of a practical system in which all of the operative componentsand subunits, whether specifically depicted or identified or not, arecompactly incorporated within a frame of relatively small dimensions. Inthis example, the pump/motor combinations are arranged such that thereturn couplings 142 extend directly outward at the access (front) sideof the frame 140. The pumps 69 lie at two levels, and includeT-couplings as well as manually operable valves that are convenientlyplaced at the front of the frame. The outlet couplings for the moderatetemperature channels 55, 56, 57 are within the same interior volume ofthe frame 140 but vertically disposed alongside the end of the array ofpump/motor sets, at the right side of the vertical center of FIG. 4.

[0053] The upper pump/motor combinations are physically connected to theframe 140 at a top panel or support by upper brackets 146, whileunderside brackets 147 support the lower or central set of pump/motorcombination on supports in the mid region of the frame 140. Thisarrangement is both compact and allows the couplings to be convenientlyavailable for external connections, with adequate volume available forthe different functional units of a refrigeration system having largecapacity.

[0054] Viewed as they are located in FIG. 4, such subunits and elementscan be referred to as in “upper”, “lower”, “right” and “left” locationsfor convenience. Thus, the pressurized tank 60 for heat transfer fluidis mounted to depend from the upper right-hand side of the frame 140just above the large compressor 14 which is mounted in an upstandingposition on the floor of the frame 140. The suction accumulator 122 is asmaller tank on the right side of the frame at the floor, and coupled tothe horizontal cylindrical body 150 of the subcooler 120, with theencompassing coil 152 about the subcooler cylinder 150 leadinghorizontally through the filter 124 to the refrigerant receiver tank 123which is at the left front side of the frame 140. Behind the insulatedoutlet couplings 144 for the low temperature channels 50, 51, 52 aredisposed a row of evaporator/heat exchanger units 67, in the immediatefront of which are the proportional control valves 65. A referenceevaporator is also accommodated within this space between the insulatedoutlet valves 144 and the evaporator/heat exchangers 67. An oilseparator 125 is disposed on the floor of the frame 140 behind thesuction accumulator 122, and a desuperheater expansion valve 128 islocated above it, adjacent the compressor 14. The condenser 16 ispositioned to the right of the evaporator/heat exchangers 67 on the sideof the compressor 14. The heat exchangers 100 for the moderatetemperature channels are behind a vertically aligned group of solenoidvalves 102 for those channels, between the array of pump/motorcombinations and the pressurized tank 60 for heat transfer fluid. Anumber of small conduits 148 run from the outlet couplings 144 to thetop of the frame 140, where connections can be made through self-closingvalves to a purge gas source.

[0055] With this arrangement, a single, highly reliable refrigerationunit can feed branch lines to the different control units and theiroperative subsystems, and all of the necessary interconnections andthermal exchange relationships can be established in a much moreefficient configuration than was achievable. The saving in floor spaceat a semiconductor fabrication facility, which is sometimes calculatedin terms of $100,000 per square foot, is very substantial.

[0056]FIG. 5 depicts an alternative arrangement of a system for avoidingthe occurrence of the astable condition in a proportional control valvesystem referenced above.

[0057] In this arrangement, a reference evaporator 94 fed by a capillary93 with subcooled refrigerant is used in parallel with a manifold 92feeding the three branches constituting temperature control channels 50,51, 52 containing separate flow control valves (TXVs) 65. The pressuresin temperature responsive bulbs 82, 82′, 82″ associated with thereference evaporator 94 are communicated by standard coupling conduitsto control the refrigerant flow through the flow control valves (TXVs)65, as previously described. The evaporators 67 in the channelsdesignated I, II and III and numbered 50, 51 and 52, each control thedegree of chilling of the heat transfer fluid in the heat exchangerswithin the evaporator/heat exchanger combinations 67 (best seen in FIG.1). Thereafter, the outputs of the evaporators 67 are fed to the outputmanifold 95, and returned to the refrigeration unit 12.

[0058] In this system, however, control of the flows of subcooledrefrigerant through the flow control valves 65 is regulatedelectronically, using the relationship between the temperatures of theindividual evaporators 67 and the reference evaporator 94. Athermocouple or other temperature sensor 110 is responsive to thetemperature level at the reference evaporator 94 outlet. Separatetemperature sensors 112, 113 and 114 provide indications of theindividual superheat levels at the outputs of the evaporators in theseparate channels 50, 51, 52. Each of the sensed temperature signalsfrom the individual branch sensors 112, 113 and 114 is compared, incomparator circuits 116, to the reference evaporator superheat level asmeasured by the sensor 110. Thus, three superheat difference temperaturelevels are provided to individual subtraction circuits 117, 118 and 119.These subtraction circuits 117, 118 and 119 are individually also incircuit with the temperature command outputs T_(vI), T_(vII) andT_(vIII) from the controller 40 and supply control signals to theheaters 90, 90′ and 90″ at the bulbs 82, 82′, 82″ which govern thepressure and therefore the flow through the flow control valves 65. Thecomparator circuits 116 respond to the difference (Δ_(T)) between theevaporator superheat in each branch and the reference evaporatorsuperheat. As long as that difference Δ_(T) is greater than 10° C., nocorrection is made in the heater command temperature that controls flow.If the Δ_(T) value is 10° C., then the subtraction circuits 120-122reduce the heater driving temperature by 1° C. The subtraction value isincreased by 1° C. for each 1° C. difference in Δ_(T), changing in alinear manner until the heater driving signal is reduced by 10° C. for aΔ_(T) difference of 0° C. In this mode of operation, flow into anevaporator is automatically throttled down if the superheat lowers to alevel that approaches the superheat level established as a virtualconstant by the reference evaporator. Consequently, the branchevaporators cannot reach the astable condition of operation.

[0059] The problem of flushing all heat transfer fluid out of the tooland the lines connecting to the tool, prior to removal of the tool fromthe cluster, involves more complexities than are superficially evident.Given that the heat transfer fluid must remain in the liquid state andundergo limited viscosity change across a wide temperature range fromnormal freezing to normal boiling, one of the perfluorinated or glycolcompounds is usually, if not necessarily, used. These commercial mixesare expensive but in the past it has been regarded as inevitable thatsubstantial amounts have been flushed or leaked onto the floor of theprocessing facility. Avoiding any significant loss of fluid, minimizingdown time for tool disconnection and replacement, and assuring fullflushing of the lines and a simplified sequence of operations arehowever of meaningful importance. The diagram of FIG. 6 shows how thisis accomplished in each channel of the present system, where thetemperature control unit 10 that receives refrigerant from therefrigeration unit (not shown) is coupled to its associated tool 28. Aninlet or return coupling 180 includes a manual control 182 such as amanually operable handle for receiving the return flow on an insulatedline 184 from the tool 28. An outlet coupling 186 also having a manualon/off control 188 is coupled via an insulated line 190 to the input tothe tool 28 to complete the circulation loop for heat exchange fluid.The outlet line 190 includes the lowest point in the loop, which is wellbelow the lowest point in the internal pathway to the tool 28, which isat a higher elevation.

[0060] From the return coupling 180, a small branch line 194 including arelief valve 195 leads to a recovery sight glass 196 for viewing bubblesin the fluid passing therethrough. The line 194 and sight glass 196 arecoupled to a first input port 198 to the reservoir 60. This forms onepath for forcing heat transfer fluid back into the reservoir 60.Separate detachable lines 200, 201 (shown by dotted lines) are adaptedto be coupled to points in the conduits and to be used for either gas orliquid transfer under pressure. A pressurized tank 191 of inert gas(e.g., nitrogen) can be selectively coupled by a detachable line (notshown) to either of two different purge valves 202, 208 during differentsteps in the operation. A first purge valve 202 is coupled to a lowpoint in the line 190 and can be connected via the detachable line 200to a second input 210 to the pressurized fluid tank 60. The second purgevalve 208 is located close to the input to the tool 28 in the line 184,and is be connected, at an appropriate step in the procedure, to thepressurized N₂ tank 191.

[0061] The operation of the flush and fill system is carried out for agiven tool during down times of that tool in the cluster tool operation.Because of the extreme precision required for various tools insemiconductor fabrication, most tools incorporate some subunits withextremely tight tolerances. These tolerances cannot be maintained withextended use and wear, and thus the tools can have a finite lifetime ofa few hundred hours or more. Consequently, the tools periodically haveto be taken off line for replacement of critical parts or refurbishment.A new or replacement tool is put into position or the tool is returnedto service after quick corrective action. Down time usually occurs on aregularly scheduled basis, but can happen irregularly if inspectionshows a drop off in product quality.

[0062] When disconnection and flushing of a tool is to take place, thefirst step, after turning off the pump 69, is to close the returncoupling 180 and the outlet coupling 186, using the manual controls 182,188, respectively. The detachable line 200 is coupled between the firstpurge valve 202 and the top input port 210 to the tank 60. A gas linefrom the pressurized nitrogen source 191 is coupled to the second purgevalve 208, and a gas pressure of 25-50 psi, which is greater than thepressure of 2-20 psi in the fluid tank 60, is applied. This effectivelyforces the heat transfer fluid in reverse direction from a pointadjacent the tool, through and out the tool 28, past the low point inthe outlet line 190 and back through the first purge valve 202 and thedetachable line 200 into the tank 60. This is continued until the tool28 is empty. The return line 184 and coupling 180 are then flushed afteropening the return coupling 180, by applying purge gas pressure at thesecond purge valve 208 with the line 200 disconnected. The pressureforces any fluid in the return line 184 and return coupling 180 backthrough the pump 69 and a small branch line 212 into the sight glass andto the tank port 198. When bubbles appear in the recovery sight glass196, or no liquid remains in the flow, the valve at the return coupling180 is closed and the pressurized gas source 191 is shut off, completingthe purge. This two step procedure is quick and convenient and assuresagainst spillage.

[0063] As noted, the use of the low point in a connecting line assuresadequately complete flushing in the shortest practical time, even thoughthe fluid is being returned to a pressurized tank.

[0064] The connections of the coupling lines 184, 190 between the tool28 and the return coupling 180 and outlet coupling 188 can then bedisengaged, with only immaterial leakage of heat transfer fluid, if any.After reconnecting a tool, whether the same tool or a replacement, viacoupling lines to the two couplings 180, 186, the refill operation canbe started.

[0065] The return and outlet couplings in the valves 180, 186 areopened, after opening the second purge valve 208 to atmosphere. A smallpurge cup (not shown) may be kept available to receive any outflow offluid. The pressure in the tank 60 may be augmented by gas underpressure coupled to the port 210 from the source 191. Gas pressure underthese conditions drives heat transfer fluid through the line 194 fromthe port 198, through the outlet coupling 186, the line 190, the tool28, the return line 184 and the line 190 and the tool 28. Fluid fillsthe lines and reaches the open second purge valve 208 until it begins toflow out, as into the purge cup or an absorbent pad. When this happens,the flow can be stopped and the vent closed at the second purge valve208. The detachable line 201 is then attached between the port 210 atthe top of the tank 60 and the second purge valve 208, and the pump 69is started and run for approximately five minutes. The detachablecoupling 201 can then be disconnected, with the conduit loop being readyfor return to operation. The gas pressure utilized is usually in the25-50 psi range during the flush operation, while the pressure in thefluid tank 60 is held at, or brought to the range of 2-20 psi during thefill step. This operation therefore not only assures adequately completeflushing in a short time, but easy and almost automatic filling, withonly a small amount of liquid being released into a container in orderto assure freedom from trapping gases internally.

[0066] The pressurized tank for heat transfer fluid offers otheradvantages, inasmuch as it maintains balance in the system. By keepingthe lines filled with replenishment fluid in the event there is any lossor leakage, the pressurized system limits any tendency of the pumps tocavitate due to inadequate liquid or pressure in the lines. The coolantsused include those perfluorinated compounds sold under the trademarks“Gaulden” and “Fluorinet”. In the compact motor/pump combination, thesecoolants are used as hydrodynamic bearing fluids within an enclosedrotor, so as to ensure longer life under virtually continuous operation.

[0067] Referring to FIG. 7, the geometry of another system in accordancewith the invention is shown having superior operating versatility whileat the same time requiring only limited floor space. What is shown inFIG. 7 is a system which, with a like frame and refrigeration unit tothe FIG. 4 system, can provide 1, 2 or 3 temperature control channels.In this system, one or two of the channels can be chilled (here operatedto a minimum temperature of −40° C.) or heated while the unchilledchannel or channels can be operated from ambient temperature toapproximately 100° C. or more. Furthermore, all temperatures can againbe separately controlled, as described in the previous example. Apractical system of this type has a length of 36 inches, a height of 30inches and a depth of 14 inches and is designed such that the units canbe stacked two high. Stacked two high to provide a maximum capacity ofsix channels, the footprint is less than 0.6 ft.² per channel. Thisversatility allows the semiconductor fabrication facility to adapt thetemperature control units to a wide variety of cluster tools.

[0068] The configuration of FIG. 7, using single chilled channel canoperate with a 1.5 KW refrigeration capacity, provided by an upstandingcompressor 14 at one side of the base of the frame 140′. The sameadvanced refrigeration functions are included, comprising a horizontallymounted subcooler 120, filter 124, and bypass and desuperheat functionsobscured behind a refrigerant receiver 123 at one side of the base ofthe frame 140′. One or two compact evaporators 67 for the chilledchannel or channels, and heat exchangers for the unchilled channels, arealso mounted on the floor of the frame 140′. Again, heating functionsare made available for all channels.

[0069] As seen in FIG. 7, the valve and port connections to exteriorlines (not shown) for the passage of coolant to a fabrication tool aredisposed along a side access plane of the frame 140′. Because only threechannels are used at a maximum, the side of the frame is adequate inarea for these connections, which are made possible because the threemotor 72 and pump 69 combinations are mounted horizontally, inside-by-side relation and do not require either substantial length orwidth. An upper corner of the frame 140′ is occupied by the pressurizedreservoir 60 for heat transfer fluid, and the unit includes the samecapability as previously described for flush and fill operations in eachchannel.

[0070] Although there have been described above and illustrated in thedrawings a number of forms and modifications in accordance with theinvention, it will be appreciated that the invention is not limitedthereto but encompasses all expedients and variants in accordance withthe appended claims.

1. A system for controlling the temperature levels of a number of toolsdeployed in a cluster and providing different fabrication functions fora product being manufactured, comprising: a single refrigeration unitproviding subcooled pressurized refrigerant and including a singlecompressor having capacity adequate for chilling all the toolsconcurrently desired individual levels; a pressurized reservoir forthermal transfer fluid; a source of unchilled coolant; a plurality ofcontrol channels, each including heat exchanger means, a fluid pump, andfluid heater means disposed to define a separate thermal transfer fluidloop in communication with a different tool, and with the thermaltransfer fluid reservoir, the control channels comprising at least firstand second types, control channels of a first type each having its heatexchanger means coupled to receive the subcooled refrigerant from therefrigeration unit and controllable evaporator means coupled to supplyrefrigerant to the associated heat exchanger means, control channels ofthe second type being coupled to receive the unchilled coolant at theheat exchanger means therein; and regulator means responsive to thetemperature of the different tools and coupled to operate the controlchannels to provide thermal transfer fluid in each channel at atemperature to maintain each respective tool at its selected temperaturelevel.
 2. A system as set forth in claim 1 above wherein the regulatormeans comprises servo control means for each control channel, eachincluding means for sensing the tool temperature, means for generating acontrol signal representative of the difference between actual anddesired tool temperature, and means for controlling the heaters in eachcontrol channel, the evaporators in channels of the first type, and theunchilled fluid flow in channels of the second type, to maintain thedifferent tool temperatures at desired levels using the thermal transferfluid in the associated loop.
 3. A system as set forth in claim 1 above,further including valve means disposed in the control channels forselectively shutting off flows in the loops, and further including meansin each of the control loops for injecting gas to purge fluid in theindividual control loop only.
 4. A system as set forth in claim 1 above,including supply and return manifolds coupling each of the control unitsof the first type to the refrigeration unit.
 5. A system as set forth inclaim 3 above, wherein the refrigeration unit includes a condensercoupled to the compressor output, the condenser being coupled to thesource of unchilled coolant for reducing the temperature of pressurizedrefrigerant from the compressor, and a subcooler coupled to the outputof the condenser for passing the pressurized refrigerant in thermalinterchange relation with low pressure returned refrigerant.
 6. A systemas set forth in claim 5 above, wherein the compressor includes aninjection capillary tube coupled to the condenser output, hot gas bypassvalve means coupling the output of the compressor to the input, anddesuper-heater expansion valve means coupling the output of thecondenser to the compressor input.
 7. A system as set forth in claim 1above, wherein the source of unchilled coolant comprises a water feedsystem for utility water and wherein the control channels of the secondtype include valve control means coupled in the coolant path to the heatexchanger means for controlling the flow of unchilled coolant in on-offfashion.
 8. A system as set forth in claim 1 above, wherein the heatexchangers in the control channels of the first type provide thermalenergy interchange between the evaporated refrigerant and the thermaltransfer fluid passing from the evaporator in the flow path toward thetool, and wherein the control channels of the first type further includea proportional control valve responsive to a control signal from theregulator means for controlling flow rate through the associatedevaporator means.
 9. A system as set forth in claim 1 above, wherein thecontrol channels of the first type cover a temperature range from about−40° C. to about +100° C., and wherein the control channels of thesecond type cover a temperature range from the temperature level of theunchilled coolant to approximately +100° C.
 10. A system as set forth inclaim 1 above, wherein the pumps comprise motor/pump combinations, eachconcentric with a different horizontal axis in the array, with themotors being coaxial with the respective pumps, and the pumps beingaligned in a common plane transverse to the axes of rotation, the pumpsand the associated conduits in the channels of the first type includingexterior insulation means.
 11. A control loop system for maintaining thetemperature of an operating tool at a selected level within asubstantial temperature range that includes levels above and below theambient, using a chilled pressurized refrigerant and a thermal transferfluid, comprising: means defining a control loop for a thermal transferfluid communicating in thermal interchange relation with the tool, theloop further including pump means for the thermal transfer fluid;electrical heater means disposed in the control loop between the pumpand tool and controllable in response to an energizing temperaturecontrol signal; heat exchanger means in the loop and receiving thethermal transfer fluid and the chilled refrigerant; proportional valvemeans coupled to receive the chilled refrigerant in the heat exchangermeans for controlling the flow of chilled refrigerant in the heatexchanger means such as to maintain a selected below ambient temperaturein the thermal transfer fluid transferred to the tool, and means coupledto the heater means for controlling the heater means to alternativelymaintain a selected temperature level that is above the ambient in thethermal transfer fluid.
 12. A system as set forth in claim 11 above,wherein the refrigerant is a subcooled refrigerant and the control loopsystem receives the refrigerant and wherein the heat exchanger meansincludes an internal evaporator coupled to receive the refrigerant at arate controlled by the proportional valve means and providing avaporized refrigerant at a temperature to cool the thermal transferfluid to a selected level.
 13. A system as set forth in claim 11 above,wherein the proportional valve means comprises a proportional integralderivative system including a valve element means for controllingrefrigerant flow rate to the evaporator, the proportional valve meanscomprising chambers defining first and second interior volumes confininga pressurized gas and including an interconnecting gas conduit, and thechamber defining the first volume being in thermal communication with athermal energy source controlling the internal pressure in the firstinterior volume, the chamber defining the second interior volumeincluding a flexible diaphragm and a valve stem, the flexible diaphragmforming a moveable wall of the second interior volume, the valve stemcontrolling refrigerant flow in accordance with its position, and beingcontrolled in position by the pressure in the second interior volume.14. A system as set forth in claim 11 above, wherein the fluid pumpmeans comprises a pressurizing pump having an inlet and outlet, andwhere the system further includes conduits coupling thermal transferfluid from the control loop system to the tool whose pressure is to bemaintained, and valve means at the input and output lines at the controlloop subsystem, for selectively closing off the inlet and outlet lines,and wherein the system includes pressurized gas injection means coupledto the control loop system such that thermal transfer fluid can bedriven out of the conduits and a selected tool, and the conduits andtool can be isolated for maintenance or replacement purposes.
 15. Asystem for separately controlling the temperature of a number ofcontrolled units using heat transfer fluid and comprising: a supplyreservoir providing pressurized heat transfer fluid; a singlerefrigeration unit providing high pressure refrigerant; a number ofconduit loops receiving refrigerant from the refrigeration unit and heattransfer fluid from the reservoir and coupled to circulate heat transferfluid through the associated controlled unit, each of the conduit loopsalso including an evaporator receiving the refrigerant from therefrigeration unit and a heat exchanger for interchanging thermal energybetween the heat transfer fluid and the refrigerant; servo control meansfor each of the conduit loops, each servo control means storingtemperature values desired for the controlled units and including meansfor sensing the actual controlled unit temperature and providing acontrol signal to indicate a needed correction; and a number ofproportional control valves, each disposed in a different conduit loopbetween the refrigeration unit and the evaporator for controllingrefrigerant flow thereto in response to the control signals, to maintainthe temperatures of the heat transfer fluid and the controlled units ata desired level.
 16. A system as set forth in claim 15 above, whereinthe conduit loops each include a pressurizing pump, and a closely spacedmotor coupled to and drive the pump, and wherein the motor is collinearwith the pump and coupled by a common shaft and includes a separatingpump mount thermally isolating the pump from the motor, and wherein themotor includes a shaft hydrodynamically supported by pressurized heattransfer fluid at substantially constant temperature.
 17. A system asset forth in claim 14 above, wherein the refrigeration unit has arefrigeration capacity at a predetermined temperature level that issufficient to meet the total refrigeration demand of all of the conduitloops, and wherein the temperature variations in the heat transfer fluidcan be in excess of +100° C.
 18. The system as set forth in claim 14above, wherein the system receives cooling fluid from an unrefrigeratedsource, and wherein the heat exchangers comprise a first type providingthermal interchange between the refrigerant and the heat transfer fluid,and a second type providing thermal interchange between theunrefrigerated cooling fluid and the heat transfer fluid.
 19. The systemas set forth in claim 14 above, wherein the conduit loops include valveconnections providing outlets to and returns from the controlled units,the valve connections including shut-off valves, and the system furtherincluding conduit lines coupling the valve connections to and from theindividual controlled units.
 20. A system as set forth in claim 19above, wherein the system includes means for providing a pressured purgegas to at least some of the conduit loops to drive heat transfer fluidfrom one or more selected controlled units and the conduit lines coupledthereto into the pressurized reservoir.
 21. A system occupying a lowvolume, but providing adequate refrigeration capacity and temperaturecontrol for individual tools having varying temperature maintenancerequirements, while permitting convenient coupling and servicing,comprising the combination of: a rectangular open-sided frame forcontaining all the interior units; a single refrigeration unit mountedwithin the frame and having a refrigeration capacity substantially equalat a minimum to the maximum refrigeration demand of the tools; aplurality of pump/motor combinations arrayed within the frame alongadjacent horizontal axes, the pumps being collinear with the motors; aplurality of heat exchanger units disposed adjacent the pump/motorcombinations, the heat exchanger units being coupled in temperaturecontrol loops to different ones of the pump/motor combinations andincluding heater means in at least some of the loops, the heat exchangermeans comprising both a first type having means for cooling the heattransfer fluid only with an unchilled liquid, and a second type forcooling the heat transfer fluid with refrigerant from the refrigerationunit, wherein the lowest temperature attainable is substantially belowambient; the heat exchangers of the second type receiving refrigerationfluid in separate and parallel temperature control loops, each inthermal intercommunication with heat transfer fluid to be supplied to adifferent tool; a plurality of control means, each associated with aseparate temperature control loop for controlling the temperature of theheat transfer fluid to a different tool, and providing the heatexchangers of the first type with an on/off binary-controlled flow ofunchilled liquid, and providing heat exchangers of the second type witha proportional flow of expanded refrigerant; and wherein the systemfurther comprises a pressurized reservoir for heat transfer fluid and apressurized reservoir for refrigeration fluid feeding the parallelcontrol loops.
 22. The method of controllably regulating the separatetemperatures of at least a number of the tools in a cluster toolcomprising the steps of: passing pressurized heat transfer fluid inindividual thermal exchange relation with different separate tools;providing a single flow of refrigerant having refrigeration capacityadequate for the concurrent refrigeration maximum of at least some ofthose of the tools that are to be refrigerated below ambient level;branching the refrigerant into separate heat exchange paths in thermalinterchange relation with the heat transfer fluid, one path for eachcontrol loop associated with a tool that is to be lowered below ambienttemperature; providing separate control signals representative of thecurrent temperature level desired for the different individual tools;and individually controlling the temperatures of the heat transferfluids in each of the separate control loops by varying the temperaturesof the refrigerants in those branches to maintain the temperatures ofthe tools at their desired levels.
 23. The method as set forth in claim22 above, wherein the refrigerant is provided as a high pressuresubcooled refrigerant and wherein the step of varying the temperature ofthe refrigerant in the branches comprises evaporating refrigerant at arate in each branch responsive to the control signal for the controlloop to establish a desired lower temperature.
 24. The method as setforth in claim 23 above, wherein the tools are at times to be raised intemperature above the ambient level, and wherein the method furthercomprises the step of heating the heat transfer fluid in the controlloops in accordance with the control signals and the method furthercomprises the step of returning the refrigerant to a single flow forrecompression after evaporation.
 25. The method as set forth in claim 24above, wherein the cluster tool includes at least one tool that need becooled only to an ambient level, and wherein the method furthercomprises the steps of providing a coolant at ambient temperature level,passing the ambient temperature level in thermal interchange relationwith the heat transfer fluid for the associated at least one controlloop, and varying the temperature of the heat transfer fluid to beprovided to the at least one associated tool by varying the flow of theambient coolant in on/off fashion.
 26. A method as set forth in claim 25above, further including the step of varying the rate of evaporation ofrefrigerant in the different branches by proportional control includinga temperature responsive compressible fluid in each branch, and furtherinitiating rapid cooldown by a separate flow of low temperatureevaporated refrigerant at cooldown transitions indicated by the controlsignals.
 27. The method for controllably regulating the separatetemperatures of different devices with a single temperature control unitcomprising the steps of: passing pressurized heat transfer fluid inindividual thermal exchange relation with different ones of the devices;providing a single flow of subcooled, pressurized refrigerant adequatein refrigeration capacity to meet the demands for refrigeration of thedifferent devices; branching the subcooled refrigerant into separateheat exchange paths for the different devices; and individuallycontrolling the temperatures of the different devices by evaporating therefrigerant in the separate branches at different flow rates.
 28. Acompact unit having a low footprint area, for controlling, with heatinterchange fluids, the temperature of each of a number of differentfabrication tools which may be arranged in a cluster, comprising: anopen frame delineating an open interior volume of rectangular form andincluding a horizontal base of the requisite small footprint area andopen sides, one of which is accessible to the tools; an array of heatinterchange fluid pumps mounted in the frame, each disposed about adifferent horizontal axis in an upper region of the frame, the pumpsincluding inlets and outlets accessible at a first open side of theframe for individual coupling to the tools; a number of heat exchangersdisposed below the pump array within the frame; a common heat transferfluid tank mounted within the frame adjacent the array of pumps, andcoupled thereto; a number of temperature control conduits coupling theinlets and outlets of the different pumps to different heat exchangersin separate control loops; and a single refrigeration unit mountedwithin the frame adjacent the array and including a compressor havingadequate refrigeration capacity for the total refrigeration demand ofthe different tools, and the compressor being coupled to supply chilledrefrigerant to at least some of the heat exchangers.
 29. A unit as setforth in claim 28 above, wherein the pumps comprise motor-pumpcombinations, each motor being coaxial with its pump along its separateaxis and rotatable thereabout, the horizontal axis of the pumps beingsubstantially parallel.
 30. A unit as set forth in claim 29 above,wherein the frame has reactively broad front and back faces, one ofwhich is the first open side.
 31. A unit as set forth in claim 29 above,wherein the frame has relatively narrow open side faces and wherein theeach of the pumps in the array is disposed along a differentsubstantially parallel horizontal axis transverse to the side faces andthe inlets and outlets are disposed adjacent a single one of the sidefaces.
 32. A unit as set forth in claim 28 above, wherein at least someof the heat exchangers include evaporators receiving refrigerant, andproportional controllers in the refrigerant couplings to the evaporatorsfor controlling the flow to maintain the desired fluid temperature, theheat exchangers and evaporators being disposed below the pump array. 33.A unit as set forth in claim 32 above, wherein the unit includes meansfor receiving unchilled coolant from an external source and wherein theheat exchangers are divided into two groups, a first group includingevaporators and receiving refrigerant from the refrigeration unit, andthe second group including heat exchangers receiving the unchilledcoolant.
 34. A unit as set forth in claim 28 above, wherein the unitfurther includes separate heaters in each of the temperature controlconduits, for selectively heating the thermal transfer fluid therein.35. A unit as set forth in claim 28 above, wherein the pumps for controlconduits receiving refrigerant from the refrigeration unit are disposedin a separate lower set relative to the other pumps, and wherein theunit further includes insulation disposed about the refrigerantreceiving pumps and the associated conduits for the heater interchangefluid.
 36. A unit as set forth in claim 28 above, wherein the singlerefrigeration unit includes a compressor having approximately 10 HP forproviding approximately 4000 watts of refrigeration capacity at −40° C.for the control conduits, the unit having a footprint of approximately12″×34″.
 37. The method of removing pressurized thermal control fluidfrom a selected semiconductor fabrication tool connected by input andoutput lines to a temperature control unit including a pressurizedthermal control fluid source comprising the steps of: closing off thelines at the temperature control unit; feeding a gas under pressure intoone line in the region of a low point in the lines while coupling aregion of the other lines adjacent the tool to the fluid source to drivethermal control fluid from the low point in the first line, the tooland, from a part of the second line into the pressurized thermal controlfluid source; opening the said one line at the temperature control unit;feeding the gas under pressure into the said other line adjacent thetool to drive the thermal control fluid remaining in the said other lineand tool back into the source; and closing off both lines.
 38. Themethod as set forth in claim 37 above further including the step ofrefilling the lines and the tool with thermal control fluid includingthe steps of: opening both the first and second lines at the controlunit; venting the connected lines to atmosphere near the tool; andallowing the pressurized thermal control fluid to flow from the sourceinto the lines and the tool.
 39. The method as set forth in claim 38above, further including the steps of: determining when fluid has beendriven back toward the source through the said other line by observingthe presence of at least bubbles in the line; maintaining thepressurized thermal fluid control source at a pressure of 10-25 psi;pressurizing with a gas pressure of greater than 25 psi; and continuingthe refilling until liquid appears at the venting point.
 40. The methodof isolating a tool in a cluster tool from a source of heat transferfluid conducted to and from a control channel by a pair ofdisconnectable lines, at least one of which is below the tool,comprising the steps of: providing a source of pressurized heat transferfluid to the lines; first purging the heat transfer fluid from a part ofthe disconnectable lines by driving the fluid under gas pressure from alow region of the lines through the tool and toward the source from apoint near the tool; again purging the heat transfer fluid from a partof the disconnectable lines by driving the fluid under gas pressure fromthe point near the tool and through a part of the control channel towardthe source; disconnecting the tool from the control channel forappropriate servicing or replacement; reconnecting the tool to thecontrol channel; and refilling the control loop from the pressurizedreservoir.
 41. The method as set forth in claim 40 above, wherein thepressure of the purging gas is higher than the pressure of thereservoir, and further including the steps of venting gas from theinterior of the control loop after reconnection, and refilling theinterior loop until liquid begins to vent from the system.
 42. In asystem that provides heat transfer fluid to a number of tools inseparate loops, to provide temperature control of the loops, a subsystemfor enabling individual tools to be cleared of heat transfer fluidcomprising: a single pressurized reservoir for the heat transfer fluid;a number of control loops for individual control systems for thedifferent tools, the control loops including return ports and outletports, each having an associated flow control valve; a number of toolconduit systems, each for a different tool, and each including returnand input lines connectable to the return and outlet couplingsrespectively for the different tools, each conduit system including alow point below the tool; a number of purge gas inputs, each coupled toa different control loop conduit adjacent at least the low point:therein; a source of pressurized gas available to be coupled to thepurge inputs to the control loops; and at least one heat transfer fluidline, adapted to be coupled between the source of pressurized heattransfer fluid and a chosen one of the control loops, at the low point,whereby by coupling the source of purge gas to a purge gas input in acontrol loop, heat transfer fluid is driven out of the tool loop towardthe pressurized reservoir.
 43. A subsystem as set forth in claim 42above, wherein the conduits in the loops are of larger diameter than thepurge gas couplings and the feeder lines, and wherein the heat transferfluid pressure in the reservoir is sufficient to refill the tool loopconduits after reconnection of the return and input lines to the controlloop and opening of the flow control valves.
 44. A temperature controlunit configuration for providing multiple temperature controlled fluidlines for different tools in a cluster, each tool to be independentlytemperature controlled, while the temperature control unit occupiesminimal floor area and allows independent servicing of the tools,comprising: a frame having the desired low floor area, the frame havingat least one substantially vertical and open access side; a plurality ofpump/motor combinations arrayed within and coupled to the frame within afirst interior volume of the frame, the pump/motor combinations beingdisposed about separate horizontal axes and arrayed together adjacentthe access side; a plurality of return line couplings, each disposed onthe access side of the frame adjacent the first interior volume andcoupled to different ones of the pumps for intercoupling to thedifferent tools; a plurality of outlet line couplings disposed in avertical plane adjacent the access side of the frame and adjacent thefirst interior volume, the outlet line couplings being coupled todifferent ones of the pumps and available for intercoupling to thedifferent tools; a plurality of temperature control means disposedwithin the frame and below the first interior volume, the temperaturecontrol means including heat exchanger means; a single refrigerationunit including compressor and condenser means disposed within the frame,adjacent and to one side of the first interior volume; a refrigerationunit disposed within the frame adjacent the opposite side of the framefrom the first interior volume; a plurality of conduits couplingrefrigerant from the refrigeration unit to those of the heat exchangermeans requiring refrigeration; and a source of pressurized heat transferfluid within the frame above the refrigeration unit and coupled to eachof the heat exchanger means.
 45. The system as set forth in claim 44above, wherein the compressor is mounted on the base area of the frame,wherein the heat exchanger units receiving refrigerant includeevaporator units mounted below the first interior volume; and whereinthe system further includes a refrigerant receiver vessel mounted on thebase area of the frame on the opposite side from the compressor and onthe access side of the heat exchangers.
 46. A system as set forth inclaim 45 above, wherein the system further includes proportionalintegral derivative devices disposed on the access side of the heatexchangers and coupling the refrigerant to the evaporators, and furtherincludes solenoid valves coupling ambient cooling fluid to other heatexchangers, and disposed between the pressurized heat transfer fluidsource and the first interior volume.
 47. A compact system fordelivering thermal transfer fluid in different channels at adjustabletemperature levels to control the temperatures of different tools,comprising: a frame structure having a low area base and frame elementsextending vertically therefrom to provide containment for the componentsof the system, the frame structure having at least one vertical, open,access side; a number of adjacent pump/motor combinations disposed alongparallel rotational axes in an array in an upper region of the framestructure, the pump/motor combination having an inlet and outlet portsdisposed adjacent the access side; a refrigeration unit including acompressor mounted in a lower region of the frame structure, therefrigeration unit providing a pressurized, low temperature refrigerantin liquid phase; at least one evaporation/heat exchanger unit coupled toone of the pump/motor combinations and receiving both pressurizedrefrigerant and thermal transfer fluid in an individual channel, the atleast one evaporator/heat exchanger unit being disposed between thepump/motor array and the refrigeration unit; and at least onecontrollable thermal expansion valve disposed between the refrigerationunit and the at least one evaporator/heat exchanger unit for regulatingthe temperatures of the thermal transfer fluid thereof.
 48. A system asset forth in claim 47 above, wherein the system further comprises atleast one channel for moderate temperature cooling, and includes atleast one moderate temperature heat exchanger receiving thermal transferfluid and an ambient temperature coolant, and at least one control forregulating the thermal transfer fluid temperatures thereof, and whereinthe frame structure is of rectangular form with relatively broad sidefaces and relatively narrow end faces.
 49. A system as set forth inclaim 48 above, wherein the access side is one of the broad side facesand where the pump/motor combinations lie along axes perpendicularthereto and wherein the channels comprise a number of evaporator/heatexchanger units and a number of moderate temperature heat exchangers.50. A system as set forth in claim 48 above, wherein the access side isone of the narrow end faces and where the pump/motor combinations liealong axes perpendicular thereto and wherein the channels comprise atleast one evaporator/heat exchanger units and at least one moderatetemperature heat exchanger.
 51. A temperature control unit for couplingto a cluster of semiconductor fabrication tools to control thetemperature of each tool separately in accordance with an individualprogram for that tool, comprising: a number of temperature controlchannels, each including operative elements physically intermingled withelements from other channels, and each having a heat exchange loopcoupled to a different fabrication tool, the channels each including acommon coolant and a separate pressurizing pump for the coolant; arefrigeration system having a plurality of operative elements disposedin distributed relation among the temperature control channels, andincluding a refrigerant distribution and return system; a heat exchangesystem coupling the refrigerant distribution and return system to atleast one of the heat exchange loops, the heat exchange system alsobeing distributed among the elements of the temperature controlchannels; and the unit having all the operative elements thereofdisposed within a volume of less than about two cubic feet per channel.52. A unit as set forth in claim 51 above, wherein there are at leasttwo heat exchange loops receiving refrigerant for temperature control,and the unit occupies less than about 0.7 square feet floor space perchannel.
 53. A unit as set forth in claim 52 above, wherein the systemincludes a pressurized reservoir for the common coolant and wherein theheat exchange loops are each sealed fluid systems.
 54. A unit as setforth in claim 53 above, wherein the refrigeration system provides highpressure, relatively low temperature refrigerant, and the heat exchangesystem for each branch includes a different evaporator for receiving thecontrolled refrigerant flow for selectively cooling the temperature ofthe heat exchange fluid, and wherein at least one of the temperaturecontrol channels includes heating means in thermal exchange relationwith the heat exchange fluid.
 55. For separately controlling thetemperature of a number of processing tools with a heat exchange fluid,a method comprising the steps of: providing a flow of pressurized lowtemperature refrigerant having sufficient refrigeration capacity for thetotal concurrent needs of the processing tools; flowing the refrigerantinto different branches, one for each tool to be refrigerated;controlling the refrigerants flows in the different branches inaccordance with desired temperatures by lowering the pressure of therefrigerant in each branch to a selected individual level; andcirculating the heat exchange fluid in separate loops in thermalrelation to the tools and to the controlled refrigerant flows.
 56. Amethod as set forth in claim 55 above, further including the step ofselectively heating heat exchange fluid in selected ones of the heatexchange loops to raise the temperature of the processing tool above theambient level.